The present invention relates to an electro-optical device in which a light-shielding film is film-formed on a substrate in a multilayered structure by a sputtering method, a method of manufacturing the same, and an electronic apparatus.
Generally, in electro-optical devices, for example, liquid crystal devices which perform a predetermined display using a liquid crystal as an electro-optical material, the liquid crystal is held between a pair of substrates. Among them, in an electro-optical device, such as a liquid crystal device of an active matrix drive scheme based on a thin film transistor (TFT) drive, thin film diode (TFD) drive or the like, pixel electrodes and switching elements are provided at intersections of a plurality of scanning lines (gate lines) and a plurality of data lines (source lines), which are arranged in longitudinal and traverse directions, on a substrate (active matrix substrate).
A switching element such as a TFT element turns on by an ON signal supplied to the gate line and writes an image signal, which is supplied via a source line, to the pixel electrode (transparent electrode (ITO)). Thus, a voltage based on the image signal is applied to a liquid crystal layer between the pixel electrode and a counter electrode, thereby changing the arrangement states of liquid crystal molecules. In this way, the transmittance ratio of a pixel changes, light passing through the pixel electrode and the liquid crystal layer changes according to the image signal, thereby performing image display.
An element substrate constituting such a switching element is constructed by stacking a semiconductor layer film, an insulating film (interlayer insulating film), or a conductive film with a predetermined pattern on a glass or quartz substrate. That is, by repeatedly performing a film formation step and a photolithography step over various films, a TFT substrate or the like is formed.
In addition, light influences a TFT element such that the transistor characteristics of the TFT element changes. In particular, when the liquid crystal device is used as a light valve of a projection type display device, the intensity of incident light is very high, and thus it is important to shield a channel region or peripheral region of the TFT from the incident light. For this reason, a light-shielding film is formed to oppose the channel region or peripheral region of the TFT element, such that light is not radiated onto the channel region or peripheral region of the TFT element portion.
As a material of the light-shielding film, a metal silicide such as a non-transparent high melting point metal material or a high melting point metal compound is widely used.
In a manufacturing process, first, a conductive light-shielding film is film-formed on the entire surface of the TFT substrate by a sputtering method. Next, the light-shielding film is patterned by a photolithography method to form the light-shielding film with a predetermined pattern. And then, after an interlayer insulating film is film-formed to cover the light-shielding film, an annealing treatment is performed. Thereafter, a semiconductor layer is formed on the interlayer insulating film with a polysilicon film. Here, the annealing treatment is performed at a temperature of about 1000° C. for the planarization of the interlayer insulating film and for the contamination control of the semiconductor layer.
Further, when the light-shielding film is formed by film-forming the metal silicide, such as tungsten silicide (WSi), which is widely used as the material for the light-shielding film, by the sputtering method, at the time of the film formation, a metal single layer or amorphous layer of tungsten (W) and silicon (Si) has a high resistance value, and thus the metal single layer or amorphous layer is adversely affected from the annealing treatment to form a silicide layer which has a low resistance value.
However, when a crystalline structure of an alloy is constructed by the silicide reaction, the internal stress gradually increases. As a result, if the annealing treatment is performed in the state in which the light-shielding film (WSi), the interlayer insulating film (NSG), and, if required, the semiconductor layer (polysilicon) are deposited, when returning to room temperature after the treatment, a stress due to the thermal distortion between tungsten silicide (as the material for the light-shielding film) and NSG (as the material for the interlayer insulating film) or polysilicon (as the material for the semiconductor layer) occurs. Accordingly, cracks in the interlayer insulating film (NSG) extending from the light-shielding film are likely to be caused.
If the cracks in the interlayer insulating film is caused, the cracks spread to the peripheral region of the semiconductor layer or the like therefrom, which results in causing element defects such as electrical short or open. Therefore, the product yield is lowered.
As a countermeasure against the above-mentioned problems, a method in which the pattern of the light-shielding film is made to be small and narrow may be considered. In this case, however, light is likely to leak to the channel region or peripheral region of the TFT element portion, thus it has a little feasibility of being realized. Further, a method in which the film thickness of the light-shielding film is made to be thin may be considered. In this case, however, the sufficient light-shielding property cannot be obtained, and stepped portions with respect to other layers are likely to be caused due to the change in the film thickness.